Zest is the outermost part of the rind of oranges, lemons, limes and other citrus fruit. This part of the rind is full of tiny capsules containing a very highly flavored volatile oil, and it is this oil that gives an intense flavor to many savory dishes, sauces, cakes, desserts and preserves.
For the purest flavor, the zest must be removed from the fruit without even the smallest trace of the bitter white pith underneath it. The easiest way to do this is to use a zester or a stainless-steel potato peeler, or you can rub it carefully against the finest cutter on a grater.
Fruit that has been waxed should be washed first, very gently with a soft brush and in warm, not hot, water. Scrubbing the fruit hard can damage the skin which will then release the oil, and it will be washed away with the water.